Lecture  9    Homework  Questions

  1. Distinquish between force and pressure.


  2. State the relationship between liquid pressure and
    1. depth of a liquid
    2. density of the liquid

  3. Will the pressure be greater if you swim in fresh water or salt water at the same depth? Explain.


  4. Compare the water pressure one meter below the surface of a small pond to the water pressure one meter below the surface of a large lake. (Assume the water density is the same). Explain?


  5. In what direction does the water initially flow out of a hole punched in a container filled with water? Explain.


  6. Concerning buoyancy on a submerged object:
    1. Why does the buoyant force act upward on the object?
    2. Why is there no horizontal buoyant force on the object?
    3. When an object is completely submerged, how does its volume compare with the volume of the fluid displaced?

  7. Concerning Archimedes principle:
    1. How does the buoyant force on a submerged object compare with the weight of water displaced?
    2. If a 1-liter container is immersed halfway into water, what is the volume of water displaced?
    3. Referring to (b), what is the buoyant force on the container?

  8. What condition occurs when the buoyant force on an object is equal to the weight of the object?


  9. What happens to an object placed in a liquid when the object is
    1. denser than the liquid.
    2. less dense than the liquid.
    3. the same density as the liquid

  10. How is the density controlled for a
    1. fish?
    2. submarine?

  11. Consider a 1-ton floating ship
    1. What weight of water is displaced by the ship?
    2. What is the buoyant force acting on the ship?

  12. If the pressure in one part of a confined fluid is increased, what happens to the pressure in other parts of the fluid?


  13. Consider an hydraulic press having an output piston with a cross-sectional area of 40 cm3. If the perssure is increased by 20 N/cm3, how much extra load will be supported by the output piston?


  14. What causes surface tension?


  15. What geometric shape has the least surface area for a given volume?


  16. What determines how high a liquid will climb in a capillary tube? Include a description of the forces involved.


  17. When water faucets are turned fully on upstairs and downstairs, which faucets will have more water flow per second?


  18. Considering your body:
    1. Why does it get more rest lying down than standing or sitting?
    2. Why is blood pressure measured in the upper arm?
    3. Is blood pressure in your legs greater or less than in your arm?

  19. A water reservoir on a farm is elevated and is made of wood reinforced with metal hoops that are closer together around the bottom section than around the top section.
    1. Why is it elevated?
    2. Why are the metal hoops closer at the bottom than at the top?

  20. Consider a block of aluminum and a block of lead, each placed in a separate beaker of water filled to the brim. In both cases the water overflows. (NOTE: the density of lead is greater than the density of aluminum)
    1. If each block has the same volume, which block will displace more water?
    2. If each block has the same mass, which block will displace more water?
    3. If each block has the same weight, which block will displace more water?

  21. When standing in water at a stony beach, why do stones hurt your feet more in the shallow water than in the deeper water?


  22. Why is it not always true to say that heavy objects sink and light objects float? Support your answr using examples.


  23. If an empty ship is loaded with a cargo of styrofoam, will the ship sink deeper or rise in the water? Explain.


  24. Given two life preservers of the same size (one filled with styrofaom and the other filled with gravel) submerged in water
    1. Upon which will the buoyant force be greater?
    2. Upon which will the buoyant force be ineffective?
    If your answers are different, explain why.


  25. A half-filled bucket of water is placed on a spring scale.
    1. If a live fish is placed in the bucket, will the reading on the scale increase or remain the same?
    2. If the bucket had been filled to the brim and the fish placed in it, will the reading on the scale increase or remain the same?

    26. Calculations:

  26. In the hydraulic arrangement shown below, how much force must be used on the larger piston (area = 50 m2) to raise the 5-N object on the smaller piston (area = 1 m2)?

  27. What is the density of a 5-kg piece of metal that displaced 0.2 cubic meters of water when completely submerged?


  28. A barge that is 6 meters long and 2 meters wide floats in water.
    1. If a 500-kg box is placed on it, how much deeper will it float?
    2. How many 500-kg boxes can it carry if it can only be pushed 16 cm deeper before it sinks?

  29. What is the buoyancy force on a metal block measuring 2 m x 3 m x 5 m which is completely submerged in fluid having a weight density of 2.5 N/m3?


  30. A wooden block having a base area of 1 m2 floats at a depth of 0.2 meters. If the weight density of the fluid in which it is floating is 1.5 N/m3, what is the weight of the block?


  31. In the hydraulic system below, how much force must be placed on the smaller piston to lift a weight of 100 N on the larger piston? The cross-sectional area of the smaller piston is 0.5 m2 and the cross-sectional area of the larger piston is 10 m2.

 



Back to Assignment Sheet